This invention relates to a process for deashing coal liquids with a selective solvent extraction whereby the coal liquids and a primary selective solvent are contacted initially at a temperature greater than the temperature at which the deashing extraction occurs. A secondary selective solvent is subsequently admixed at a temperature less than that of the primary solvent admixture. After coal extract is deashed to a very low level, the coal extract may then be upgraded into more valuable products via conventional processing techniques.
The art is replete with processes for converting solid hydrocarbonaceous materials, such as coal, to mixtures of gaseous and liquid products. The following examples are representative of the many such processes. The Synthoil process, developed at the U.S. Bureau of Mines and described by Yavorsky et al. in Chem. Eng. Progress, 69, (3), 51-2 (1973), the H-Coal process, developed by Hydrocarbon Research, Inc. and described in a series of patents including Johanson, U.S. Pat. No. Re. 25,770, Schuman et al., U.S. Pat. No. 3,321,393 and Wolk et al., U.S. Pat. No. 3,338,820, and the Solvent-Refined Coal (SRC) process I and II developed by the Gulf Mineral Resources Co. and described in "Recycle SRC Processing for Liquid and Solid Fuels", presented at 4th Int. Conf. on Coal Gasification, Liquefaction and Conversion to Electricity, Univ. of Pittsburgh (Aug. 2-4, 1977), are representative. The Synthoil and H-Coal processes are generally characterized by a fixed or ebullated catalytic bed.
Recently, high pressure hydrogenation and solvent extraction techniques have been developed, the latter of which is related to the process of this invention. In the process of solvent extraction known to the prior art, crushed, finely-divided particulate coal is placed in contact with a liquid solvent which dissolves a part of the solid, usually in the presence of hydrogen gas. Following the contact, the liquid solvent and the liquefied part of the solid are separated from the remaining solid material by filtration, centrifuging or a similar operation.
One of the problems encountered in the solvent extraction method of liquefying coal has been the ability to recover the maximum quantity of coal extract while minimizing the ash content of the coal extract in order to permit subsequent conventional hydrocarbon processing techniques. A portion of this problem is that hydrocarbons adhere to and are adsorbed in the solids or ash and another portion of this problem is the difficulty of finally separating the liquid hydrocarbons from the ash. Thus the recovery of the maximum quantity of coal extract while minimizing the ash content of the coal extract is a desirable goal.
Another source of primary coal liquids which may be processed according to the method of this invention is the pyrolysis of coal. In the production of more highly refined hydrocarbonaceous products from coal pyrolysis liquids, it is also important to recover the maximum quantity of hydrocarbons while minimizing the ash content in order to permit subsequent conventional hydrocarbon processing techniques.